Electro−optic modulation of a laser beam by a traveling high−field domain in a GaAs Gunn diode

Abstract

The light beam from a GaAs injection laser (9050 Å) was modulated at 0.1 GHz by the Pockels effect of a traveling high−field domain in a GaAs Gunn diode at room temperature. The Gunn diode is 80 μm thick, 600 μm wide, and 1 mm long, and has carrier concentration of 6.3×10¹³ cm⁻³. The laser beam was focused on the center of the wider surface of the Gunn diode through a lens and a polarizer and the transmitted light was detected with a Si photodiode through an analyzer in a cross arrangement. It was found that the detected output was modulated with a S/N ratio better than 10. The Franz−Keldysh effect of the high−field domain was also measured, and a quantitative correction was made to the observed Pockels effect. It is shown that the retardation is linearly proportional to the square root of the domain voltage and also that the electric field of the domain calculated by the corrected value of the Pockels effect agrees well with the one measured by a capacitance probe.